NEC Article 440 (Air Conditioning)
What Size Breaker for a MrCool Mini Split?
The breaker, wire, MCA, and maximum breaker for every MrCool DIY 4th Gen (E Star) mini split, 9,000 to 36,000 BTU, straight from the manufacturer nameplate.
MrCool DIY Mini Split Breaker & Wire by BTU
| Unit (BTU) | Voltage | MCA | Breaker (MOP) | Min Copper Wire |
|---|---|---|---|---|
| 9,000 BTU (0.75 ton) | 115V | 19 A | 25 A | #12 Cu |
| 12,000 BTU (1 ton) | 115V | 19 A | 25 A | #12 Cu |
| 18,000 BTU (1.5 ton) | 208-230V | 18 A | 30 A | #10 Cu |
| 24,000 BTU (2 ton) | 208-230V | 22 A | 35 A | #8 Cu |
| 36,000 BTU (3 ton) | 208-230V | 28 A | 35 A | #8 Cu |
MCA, MOP, and minimum wire are the manufacturer's own figures (MrCool DIY 4th Gen E Star Installation & Owner's Manual, p.34 (Minimum Wire Gauge for Power Cables)). The breaker shown is the largest standard breaker at or below the MOP (NEC 240.6(A) / 440.22); because each MOP is already a standard size, the breaker equals the MOP. All units are single-zone. Your unit's data plate governs, and a different brand or series will differ.
Breaker & Wire for a Specific MrCool Size
The full circuit spec, the 115V-vs-240V answer, and the NEC code-minimum comparison for each MrCool DIY size.
NEC Code Minimum vs the MrCool Requirement
The wire only has to carry the MCA, so the bare NEC minimum (Table 310.16, 75°C) is smaller than what MrCool lists. MrCool sizes up for the larger breaker and for voltage-drop margin on the 208-230V runs. You must follow the manufacturer's larger requirement (NEC 110.3(B)) — the code minimum below is shown only to explain the gap, not as a wire to install.
| Unit (BTU) | MCA | NEC code min (from MCA) | MrCool requires (install this) |
|---|---|---|---|
| 9,000 BTU | 19 A | #14 Cu | #12 Cu |
| 12,000 BTU | 19 A | #14 Cu | #12 Cu |
| 18,000 BTU | 18 A | #14 Cu | #10 Cu |
| 24,000 BTU | 22 A | #12 Cu | #8 Cu |
| 36,000 BTU | 28 A | #10 Cu | #8 Cu |
The “NEC code min” column is computed from each unit's MCA through NEC Table 310.16 (75°C copper) by the same locked engine the calculator uses; the “MrCool requires” column is the manufacturer's own minimum. When they differ, the larger manufacturer value wins.
MCA & MOCP Breaker Calculator tool live, handing back the verdict with its cited source instead of a guess. Then keep the reading as one job in the Intry app.Frequently Asked Questions
What size breaker does a MrCool DIY mini split need?
Size the breaker to the outdoor unit's nameplate MOP (maximum overcurrent protection), not the BTU. For the DIY 4th Gen line MrCool prints: a 9,000 or 12,000 BTU unit takes a 25A breaker (115V, single-pole); an 18,000 BTU unit a 30A breaker (208-230V, double-pole); and a 24,000 or 36,000 BTU unit a 35A breaker (208-230V). Those MOP values are already standard breaker sizes (NEC 240.6(A)), so the installed breaker equals the MOP. Always read your own unit's data plate; a different brand or series will differ.
What size wire for a MrCool 36k mini split?
MrCool's manual specifies #8 copper minimum (#6 preferred) for the 36,000 BTU DIY, on the 35A / 208-230V circuit. Its nameplate MCA is 28A. The NEC code minimum from a 28A MCA is only #10 copper (NEC Table 310.16, 75C), but MrCool requires the larger #8 for the 35A breaker and voltage-drop margin, and the manufacturer's instruction governs the install (NEC 110.3(B)). Use #8.
Can a MrCool mini split run on a 115V circuit?
Yes, the two smallest do. MrCool's DIY 4th Gen 9,000 and 12,000 BTU units are 115V, on a dedicated 25A single-pole circuit (MCA 19A, #12 copper minimum). The 18,000 BTU and larger units step up to a 208-230V double-pole circuit. So a "1 ton" MrCool can plug into a standard 115V branch, while a 1.5 ton and up needs 240V. The nameplate tells you which.
Why is the breaker so small for such a big BTU number?
Because the DIY 4th Gen uses an inverter compressor, which draws far less than an old single-stage condenser of the same tonnage. A 36,000 BTU (3 ton) inverter mini split lands at only a 28A MCA and a 35A breaker, where a conventional 3 ton AC might want a 40-50A circuit. Size to the nameplate MCA and MOP, never to the cooling capacity.
Does a MrCool mini split need a dedicated circuit and disconnect?
Yes. MrCool's manual states the unit must be on its own individual branch circuit (never shared with another appliance), and the NEC requires a disconnecting means within sight of the outdoor condenser (NEC 440.14), which is the pull-out disconnect box mounted beside it. The small interconnect / MC cable between the indoor and outdoor unit is separate from this branch circuit and is sized per the manual's wire-gauge table.
Is the Intry MCA & MOCP breaker calculator accurate?
Every calculated figure is re-derived from its locked source before any deploy, backed by 4858 automated checks that also guard where each number comes from. A number that drifts from the cited NEC Article 440 section blocks the ship. This is our own deterministic gate, not a third-party audit. The per-tool receipt is public at https://www.intrysys.com/verified.
Go Deeper
Mini Split Wire Size (Any Brand)
Size any ductless mini split to its nameplate MCA and MOP, with typical ranges by BTU.
MCA / MOCP Calculator
Enter your unit's MCA and max breaker to get the wire, breaker, and ground.
Can My Panel Handle It?
Before you add the circuit, the NEC 220.87 check on whether the service can carry it.
R-454B Superheat & Subcooling
Charge check for the A2L refrigerant in new MrCool DIY 4th Gen systems.